Sir Agnatorian . . . . .
¿ Whyforyounogivemonitorsbrandandmodelnumber ?
¿ Whyforyouhavenewcapacitorswithfulleadsandyoutheninstalltheminthatcrudeandslipshodmanner ?
Guess that leaves me to relying on my "reading of the board" and guess that the unit is a KB monitor using a TUO8Q164 P.S. board.
With you mentioning of it working sometimes, but lately . . . that is being iffy.
I have the board markup sectioned into the AC line "HOT" portion being all within the YELLOW markup that also connects into the BLUE star power transformer within the RED rectangle, with the custom RED star switch mode driver IC # IC602 that drives this transformer.
Come back with its marked on numbering . . . as it might be needed later on, in analysis..
PLUS I have never seen THAT specific surface mount 12 pin unit being used.
On that transformers secondary, there are being two isolated / cojoined secondary windings that are marked up with BROWN and VIOLET rectangles.
They create two different DC supplies.
The BROWN feeds the D711 diode with it outputting its DC into the C711/A capacitor.
The VIOLET feeds into the D701 diode and it outputs DC into the C701 /C, C705 /D and then passes to C703/E beside the CN701 connector down at the end of the board..
TESTING . . . .
With the board dormant and having had no power applied to it for some time, initially do an ohms test across the PINK boxed mark up of the parallel-o-series connection of R609+R610 and R607 + R608 " bump up " surface mount resistors. The end to end reading should be ~1 Megohm.
(No problems being expected there . . . .)
Then plug in all connectors and power cord and set metering to DC voltage and be expecting that there will be ~320-340VDC present across the main raw DC power supply capacitior C605 / YELLOW F
. . . I'm expecting it to be there.
Then you move over to the safer lower voltage portions of the supply, first to the . . . now easily accesible "high riding" terminals of C711 A capacitor OR you can use meter ground to bare tinned Jumper Wire 3 and meter + probe to the cathode / silver banded end of D711.
Then you power up the set with its power switch to see what DC voltage you hopefully might have there now. I'm sort of expecting it to be there.
The other supply voltage to now check for will be derived from the VIOLET D701 diode.
Check for it being down at the end of board connector CN701, with either of the two black wires being used for meter DC negative and the meter DC positive lead can go to either of the 2 RED or 2 ORANGE wires . . . as they are being jumpered together... . . that is being your main DC supply, is it being present ?
IF you find both supplies outputting report back their voltages.
Plus, with both of those supplies present and operating, that will also confirm what I suspect might be your units problem.
The ORANGE boxed in component area with its 8xx series parts numbering will use the RED oval IC801 + the ALSO RED oval Power FET to supply a feedback controlled voltage, derived from the " BROWN " power supply, to the separate LED strips that provide backlighting for your frontal transmissive LCD screen.
One white LED has opened up and disabled a whole strip and the controller detects this fault and shuts down all of the strips.
IC801 pinout seems to suggest that 3 (maybe 4 ) LED backlighting / illumination strips are being used.
Your forthcoming IC 801's ID #'s will confirm.
. . . . . . .
Awaiting for your findings + supplementally needed info of . . . . .
LED's Power FET # . . . .IC801 BL controller # and main PS SMPS IC IC602 #
Curiosity question ? . . .
At the very right front bottom corners quadrant, there is being a stand alone / totally isolated circuitry path between CN702 and M501 beside the AC power plug, what is that M501 . . . . . on the sets back . . . being labeled as ?
Thaaaaaassssit . . . ..
Your . . . PHOTOGRAPH
(s) . . . . .is / are now being all marked up . . . .Ladyva sez . . .Me Too !
73's de Edd . . . . .
Remember this . . . . . you cannot achieve the impossible without occassionally attempting some of the the absurd.